Method and apparatus for hypoglossal nerve stimulation

ABSTRACT

A method of treating sleep disordered breathing in a patient includes the steps of monitoring the patient for a pre-inspiratory drive signal indicative of the breathing cycle by sensing electroneurogram activity of a hypoglossal nerve of the patient; and electrically stimulating the hypoglossal nerve of the patient following each detection of the pre-inspiratory drive signal. An implantable apparatus for stimulating a hypoglossal nerve of a patient for the treatment of sleep disordered breathing includes an electrode positioned at least partially around the hypoglossal nerve with a monitoring contact and a stimulation contact and a controller operatively coupled to the monitoring contact and the stimulation contact. The monitoring contact monitors the electroneurogram activity of the hypoglossal nerve for a pre-inspiratory drive signal indicative of the onset of inspiration and sends a signal to the controller which in turn causes the stimulating electrode to electrically stimulate the hypoglossal nerve.

CROSS-REFERENCE TO RELATED APPLICATIONS

This application claims priority under 35 U.S.C. § 119(e) fromprovisional U.S. patent application No. 60/817,907 filed Jun. 30, 2007the contents of which are incorporated herein by reference.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention is related, in general, to a method and apparatusfor the treatment of sleep disordered breathing and, more specifically,to a method and apparatus for stimulating the hypoglossal nerve of apatient for the treatment of sleep disordered breathing.

2. Description of the Related Art

Sleep disordered breathing encompasses a number of illnesses includingsnoring, upper airway resistance syndrome (UARS) and obstructive sleepapnea-hypopnea syndrome (OSAHS). Snoring occurs when there is anobstruction in the back of the mouth which causes these structures tovibrate during breathing. Upper airway resistance syndrome is a disorderthat results in an increased resistance to airflow. Obstructive sleepapnea (OSA) results in the partial or complete occlusion of the upperairways of human patients during sleep. In these patients, the upperairways obstruct as often as several times a minute with each episodelasting as long as 20-30 seconds. Each apneic episode ends with a briefarousal from sleep. Consequently, arterial oxyhemoglobin saturationdecreases drastically. Complications include excessive daytimesleepiness, restless sleep, morning headache, job-related accidents,impaired short-term memory, polycythema, hypertension, right-sidedcongestive heart failure, decreased libido, and the like. Personalitydisorder and other psychological problems may also develop over time.Obstructive sleep apnea is found in 2 to 4 percent of the population,primarily in adult men and post-menopausal women.

In humans, the hypoglossal nerve innervates the intrinsic and extrinsicmuscles of the tongue and the geniohyoid muscle. Of these musclesinnervated by the hypoglossal nerve, the genioglossus and the geniohyoidmuscles are the primary muscles involved in dilating the upper airways(UAWS). Contraction of the genioglossus muscle provides tongueprotrusion and, hence, dilates the airways.

It is generally known that the flow of inspired air is doubled bystimulation of the main branch of the hypoglossal nerve. Stimulation ofthe medial branch is nearly as effective and is superior to stimulationof other branches. Attempts have been made to improve upper airwaypatency in humans during sleep via direct electrical stimulation of thehypoglossal nerve. For instance, U.S. Pat. No. 4,830,008 to Meerdiscloses monitoring inspiratory effort followed by stimulation ofnerves associated with stimulating the upper airway muscles to treatsleep apnea. The Meer system includes an airway monitor for monitoringinspiratory effort based on sensing “action potentials” in either thediaphragm or phrenic nerve or by sensing negative pressure in the thoraxand one or more “effector” electrodes that stimulates the selected upperrespiratory muscle nerves.

U.S. Pat. No. 6,587,725 to Durand et al. discloses a method of treatingobstructive sleep apnea in a human patient. The method includes thesteps of monitoring the human patient for at least partial occlusion ofupper airways of the patient associated with obstructive sleep apnea bysensing electroneurogram activity of a hypoglossal nerve of the patient;and, directly electrically stimulating the hypoglossal nerve of thepatient when at least partial occlusion of the upper airways of thepatient occurs as indicated by the sensed electroneurogram activity ofthe hypoglossal nerve. A limitation of this method is that it onlystimulates the hypoglossal nerve if at least a partial occlusion of theupper airways of the patient occurs. Therefore, this method does notprevent occlusions from occurring.

Other methods of stimulating the hypoglossal nerve include using variousphysiological variables to synchronize the electrical stimulation withrespiration. Hypopharyngeal or espophageal pressure measurements,airflow measurements made with thermistors placed near the nose andmouth, and tracheal inter-ring distance measurements made with a straingauge are examples of physiological variables that have beeninvestigated for use in synchronization of electrical stimulation of thehypoglossal nerve and/or the genioglossus muscle. For instance, U.S.Pat. No. 5,211,173 to Kallok et al. discloses a method and apparatus forcontrolling one or more parameters of an electrical stimulationgenerator used for the treatment of obstructive sleep apnea. Sensors areused to determine the effectiveness of the stimulation. Amplitude andpulse width are modified in response to the measurements from thesensors. However, the method disclosed in this patent and other similarmethods have drawbacks and limitations.

Other treatment methods for sleep disordered breathing have included useof a nose mask through which continuous positive airway pressure isapplied to keep the upper airways open. This therapy must be continuedindefinitely, and only 60-65 percent of these patients can tolerate thetechnique long-term. Tracheostomy is another treatment for severe sleepdisordered breathing, but it is rarely used because of low patientacceptability and relatively high morbidity. Uvulopalatopharyngoplasty,removal of redundant tissue in the oropharynx, and other surgicaloperations to correct anatomical abnormalities in the upper airways canbe considered in certain cases. However, in general, all of theabove-mentioned therapies are associated with complications anddisadvantages. Weight loss may improve the condition in mild cases, butpharmacologic attempts to treat sleep disordered breathing by increasingpharyngeal muscle activity during sleep have not been found to beeffective.

SUMMARY OF THE INVENTION

Therefore, an object of the present invention is to detect apre-inspiratory drive signal by monitoring the hypoglossal nerve andusing that detection as an indication to stimulate the hypoglossal nerveto prevent airway obstruction, rather than waiting for an occlusionwithin the upper airway to occur before stimulating the hypoglossalnerve. Furthermore, the system of the present invention accomplishes theabove described objective without the use of any external sensors.

The present invention is directed to a method of treating sleepdisordered breathing in a patient. The method includes the steps ofmonitoring the patient for a pre-inspiratory drive signal indicative ofthe breathing cycle by sensing electroneurogram activity of ahypoglossal nerve of the patient; and electrically stimulating thehypoglossal nerve of the patient following each detection of thepre-inspiratory drive signal.

The method may further include amplifying the sensed electroneurogramactivity of the hypoglossal nerve to obtain an amplifiedelectroneurogram signal; and using the amplified electroneurogram signalto trigger the direct electrical stimulation of said hypoglossal nerve.The hypoglossal nerve may be monitored continuously for thepre-inspiratory drive signal, and the hypoglossal nerve may beelectrically stimulated after a preset period of time elapses fromdetection of the pre-inspiratory drive signal.

The method may also include sensing a body position of the patient; andinitiating monitoring of the patient when the patient is determined tobe in a lying down position, or more particularly, a specific lying downposition. The specific lying down position may be a supine, prone, orside-lying position.

The method may further include connecting a stimulating nerve electrodeto the hypoglossal nerve so that the nerve electrode at least partiallyencircles the hypoglossal nerve. The stimulating nerve electrode mayalso include at least first and second contacts and the step ofelectrically stimulating the hypoglossal nerve comprises passingelectrical stimulation pulses between first and second contacts of thenerve electrode and through tissue of the hypoglossal nerve. Theelectroneurogram activity of the hypoglossal nerve may be sensed with athird contact of the nerve electrode.

The present invention is also directed to a method of stimulating ahypoglossal nerve of a patient for the treatment of sleep disorderedbreathing. The method includes a first step of monitoring thehypoglossal nerve of the patient. Next, a pre-inspiratory drive signalis detected from the hypoglossal nerve indicative of the breathingcycle. Finally, the hypoglossal nerve is electrically stimulated inresponse to the detected pre-inspiratory drive signal to preventocclusion of the patient's upper airway. The pre-inspiratory drivesignal is generated by the central nervous system and propagated to thehypoglossal nerve prior to the onset of inspiration.

The present invention is further directed to an implantable apparatusfor stimulating a hypoglossal nerve of a patient for the treatment ofsleep disordered breathing. The implantable apparatus includes an cuffpositioned at least partially around the hypoglossal nerve and having amonitoring contact adapted to sense the electroneurogram activity of thehypoglossal nerve and at least one stimulating contact adapted toelectrically stimulate the hypoglossal nerve. The implantable apparatusalso includes a controller operatively coupled to the monitoring contactand the stimulation contact device. The monitoring contact monitors theelectroneurogram activity of the hypoglossal nerve for a pre-inspiratorydrive signal indicative of the onset of the breathing cycle and sends asignal to the controller. The controller operates to cause thestimulating electrode to electrically stimulate the hypoglossal nerve inresponse to the pre-inspiratory drive signal to prevent occlusion of thepatient's upper airway.

The implantable apparatus may further include a position sensing deviceadapted to determine when the patient is in a lying down position. Theposition sensing device may be adapted to determine whether the patientis in a supine, prone, or side-lying position. The controller, themonitoring contact of the cuff, the at least one stimulating contact ofthe cuff, or any combination thereof may be turned off when the positionsensing device determines that the patient is in a position other thanthe lying down position. The position sensing device may be anaccelerometer. The implantable apparatus may also further include awireless communication link associated with the controller forcommunicating with the controller form outside the patient's body, and abattery for supplying power to the controller and electrode contacts.The battery may also be rechargeable from outside of the body. Anamplifier may also be provided for amplifying the pre-inspiratory drivesignal.

These and other features and characteristics of the present invention,as well as the methods of operation and functions of the relatedelements of structures and the combination of parts, will become moreapparent upon consideration of the following description and theappended claims with reference to the accompanying drawings, all ofwhich form a part of this specification, wherein like reference numeralsdesignate corresponding parts in the various figures. As used in thespecification and the claims, the singular form of “a”, “an”, and “the”include plural referents unless the context clearly dictates otherwise.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a diagrammatic illustration of an implantable apparatus forstimulation of the hypoglossal nerve for the treatment of sleep apnea inaccordance with the present invention;

FIG. 2 graphically illustrates the flow of air during a patient'sinspiratory cycle and the corresponding electroneurogram activitymeasured at the hypoglossal nerve;

FIG. 3 is a flow-diagram of a method of treating sleep disorderedbreathing in a patient in accordance with the present invention; and

FIG. 4 is a perspective view of the cuff in accordance with the presentinvention.

DETAILED DESCRIPTION OF THE EXEMPLARY EMBODIMENTS

For purposes of the description hereinafter, spatial orientation terms,if used, shall relate to the referenced embodiment as it is oriented inthe accompanying drawing figures or otherwise described in the followingdetailed description. However, it is to be understood that theembodiments described hereinafter may assume many alternative variationsand embodiments. It is also to be understood that the specific devicesillustrated in the accompanying drawing figures and described herein aresimply exemplary and should not be considered as limiting.

The present invention is directed to a system and method for thetreatment of sleep disordered breathing through stimulation of thehypoglossal nerve of a human patient. The system and method overcomevarious shortcomings of prior art systems by monitoring the hypoglossalnerve and stimulating the hypoglossal nerve in response to apre-inspiratory drive signal before any occlusion of the upper airway ofthe patient has occurred.

With reference to FIGS. 1 and 4, an implantable apparatus 1 forstimulating a hypoglossal nerve 3 of a patient for the treatment ofsleep disordered breathing includes an cuff 5 positioned at leastpartially around hypoglossal nerve 3 and having a monitoring contact 7adapted to sense the electroneurogram activity of the hypoglossal nerve3 and a stimulating contact 9 adapted to electrically stimulate thehypoglossal nerve 3. The device further includes at least one groundcontact 10 to complete the electrical circuit for monitoring contact 7and stimulating contact 9. Together, monitoring contact 7 and groundcontact 10 forms a monitoring electrode. Similarly, stimulating contact9 and ground contact 10 forms a stimulating electrode. As shown in FIG.4, each electrode may have a separate ground contact. Alternatively,both electrodes could utilize the same ground contact. In addition, asingle stimulating electrode and a single monitoring electrode aredepicted which interface circumferentially about the hypoglossal nerve.However, the present invention contemplates that multiple electrodescould be used for redundancy and/or to target a particular region of thehypoglossal nerve. In another alternative embodiment, the cuff may haveone or more monitoring contacts 7 and stimulating contacts 9. However,rather than using a specific ground contact, this embodiment utilizesthe cuff body 16 as the ground.

Cuff 5 acts as both hypoglossal nerve stimulation electrode and ahypoglossal nerve activity sensor as described in full detail below.Implantable apparatus 1 is adapted for total implantation in the patientbeing treated without the need for associated external components. Thoseof ordinary skill in the art will recognize that cuffs other than thecuff illustrated may be used without departing from the overall scopeand intent of the present invention. For instance, the present inventioncontemplates that the cuff 5 may be U-shaped as disclosed in U.S. Pat.No. 5,344,438. The contents of which are hereby incorporated byreference. However, it can be readily recognized by one of ordinaryskill in the art that use of this cuff would require modification toinclude both a stimulating electrode and a monitoring electrode.Alternatively, the cuff may have a corrugated shape as disclosed in U.S.Pat. No. 5,634,462. The contents of which are hereby incorporated byreference. The cuff may be constructed to have a flat interface asdisclosed in U.S. Pat. No. 6,456,866. However, a variety of otherelectrodes may be used without departing from the scope of the presentinvention.

As seen in FIG. 1, implantable apparatus 1 further includes an interfacecircuit 11, an amplifier 13 and a controller 15. Interface circuit 11receives hypoglossal nerve electroneurogram activity input frommonitoring contact 7 of cuff 5 and supplies a hypoglossal nerve activitysignal to amplifier 13. Amplifier 13 supplies an amplified and filteredhypoglossal nerve activity signal to controller 15. Controller 15processes the amplified and filtered hypoglossal nerve activity signaland looks for a pre-inspiratory drive signal. Preferably, thepre-inspiratory drive signal is a spike in the hypoglossal nerveactivity signal that is generated by the central nervous system andpropagated to the hypoglossal nerve prior to the onset of inspiration.Alternatively, the pre-inspiratory drive signal may be any detectablefeature of the electroneurogram activity indicative of the breathingcycle. For instance, the drive signal may be a spike of activity or theabsence of activity.

When controller 15 detects the pre-inspiratory drive signal, it outputsa trigger signal to interface circuit 11. Once interface circuit 11receives the trigger signal, it outputs a stimulation pulse tohypoglossal nerve 3 by way of the stimulating contact 9 of cuff 5.Stimulating contact 9 of cuff 5 includes a first contact and a secondcontact arranged on hypoglossal nerve 3 to pass electrical stimulationpulses through the tissue of hypoglossal nerve 3. In this manner,implantable apparatus 1 has the ability to stimulate hypoglossal nerve 3in response to a pre-inspiratory drive signal prior to each breath.Therefore, implantable apparatus 1 prevents occlusions of the upperairway of the patient before such an occlusion has occurred.

Implantable apparatus 1 may further include a position sensing device,such as, but not limited to an accelerometer 17, adapted to determinethe body orientation of a patient. Accelerometer 17 is operativelycoupled to controller 15 and allows controller 15 to provide differentstimulation parameters to be executed based on the position of thepatient. Accelerometer 17 determines body orientation of a patient withrespect to gravity. Because sleep disordered breathing can be highlydependant on position (supine in particular), in certain patients it maybe desirable to intensify the hypoglossal stimulus when the patient isin the supine position. In fact, in certain patients it may be knownthat sleep disordered breathing is much reduced or not present whenlying on the side or front (prone) position, and the stimulation can bereduced or turned off if the patient is in that position. This datawould allow for different stimulation parameters to be executed forsupine positions versus prone or side sleeping. Accelerometer 17 mayalso be adapted to terminate therapy when the patient is detected to beupright.

In an alternative embodiment, the use of an accelerometer 17 as theposition sensing device allows implantable apparatus 1 to utilize asingle sensor assess several parameters that are useful in controllingthe therapy delivered by the system. In such an embodiment,accelerometer 17 has a wide bandwidth and is capable of measuringacceleration, motion, and/or vibration from nearly DC, for example, andwithout limitation, 0 Hz to acoustic frequencies for example, andwithout limitation, 5-20 kHz. Such an accelerometer 17, allowsimplantable apparatus 1 to determine physiological parameters such as,but not limited to, body orientation, patient movements, airwayvibration and ballistocardiogram.

Body orientation, patient movements and airway vibration can bedetermined by sampling the relative frequency spectra of the signal(low, medium, and high) produced by accelerometer 17 relative to oneanother. Generally, low frequency is under about 0.1 Hz. Mediumfrequency is about 0.1 Hz to about 10 Hz. High frequency is about 10 Hzto about 20 kHz. However, these ranges are only provided as examples andare not intended to limit the present invention. These ranges can beadapted based on the patient being treated. For example, if valuableairway vibration information is contained in lower frequencies, theupper cutoff for patient movements could be reduced.

The four previously mentioned parameters will be specifically discussedhereinafter. Body orientation, as discussed previously, can bedetermined with respect to gravity through the use of accelerometer 17.Since sleep disordered breathing can be highly dependant on position(supine in particular), in certain patients it may be desirable tointensify stimulation of hypoglossal nerve 3 when the patient is in thesupine position. In fact, in certain patients it may be known that sleepdisordered breathing is much reduced or not present when on the side orfront, and the stimulation can be reduced or turned off if the patientis in that position. This information would allow for differentstimulation parameters to be executed for supine positions versus proneor side sleeping. Accelerometer 17 also may be used to provide a signalto controller 15 to terminate therapy when the patient is detected to beupright. In addition, the accelerometer input may be used to controlstimulation. For instance, an accelerometer may be used to detect thebreathing cycle. Once the breathing rate has been identified, apredictive algorithm may be used to synchronize stimulation with thedetected breathing cycle. Of course, as noted above, the stimulationsignal may precede or lag the onset of inhalation as deemed appropriateto maximize the therapeutic benefit provided by this device. Use of anaccelerometer input may be used as an independent detector to solelymonitor breathing. Alternatively, the accelerometer may be used inconjunction with the monitoring electrode to provide a device thatmonitors both the pre-inspiratory signal and the breathing cycle.

Regarding patient motion, it is well known in the field of actigraphythat patients showing no movement may be considered to be asleep.Accordingly, patient motion, as determined by accelerometer 17, isimportant in the determination of sleep/wake state, and is thus used toturn on and turn off implantable apparatus 1. Patient motion data mayalso be communicated to the health care provider via communication link23 to establish whether implantable apparatus 1 is adequately benefitingthe patient.

Regarding airway vibration, airway instability manifests itself asvibration which is transmitted through the soft tissues of the airwayand neck. Accelerometer 17 can be configured to detect airwayvibrations. The signal produced by accelerometer 17 can be processed ina well-known manner (e.g., total power per unit time and thresholded) bycontroller 15 to detect an impending, developing or in-progressocclusion or snore. The ability to monitor vibration in the airway viaaccelerometry can be used together with hypoglossal nerve 3 activity toobtain higher degrees of reliability for proper control of implantableapparatus 1.

Finally, a ballistocardiogram may be part of the signal output byaccelerometer 17, and may be extracted therefrom. The ballistocardiogramindicates the beating of the heart, and can be used to provide cardiacparameters such as heart rate, heart rate variability, and certainarrhythmias. These are clinically important because sleep disorderedbreathing has been shown to cause cardiovascular stress through thesympathetic nervous system activation and intra-thoracic pressuremodulation. The frequency spectrum of the ballistocardiogram may overlapone or more of the frequency spectra of the body orientation signal, thepatient movement signal or the airway vibration signal. Accordingly,specialized adaptive filters (not shown) may be required to remove thefrequency spectrum of the ballistocardiogram from the overlappingspectra from the body orientation signal, the patient movement signal orthe airway vibration signal.

While the position sensor has been described hereinabove as anaccelerometer, this is not to be construed as limiting, as the use ofany suitable position sensing device has been envisioned.

Implantable apparatus 1 also includes a power supply 19 and an externalprocessing device 21. Power supply 19 is desirably a rechargeablebattery that is rechargeable from outside of the patient's body viainductive power coil technology. A two-way wireless communication link23 is associated with controller 15 for communication between controller15 and external processing device 21. External processing device 21 hasthe capability of receiving data from controller 15 and transmittingdata to controller 15 via communication link 23. In this manner, aclinician can evaluate physiological data accumulated by implantableapparatus 1 and maintenance can be performed thereon. Furthermore,physiological data accumulated by implantable apparatus 1, analyzed datasuch as, but not limited to, sleep state, and system data such as, butnot limited to, charge status and electrode impedance can all betransmitted via communication link 23 to external processing device 21for further processing and storage on a memory device (not shown)thereof.

Implantable apparatus 1 may further include a titrating subsystem (notshown). The titrating subsystem is an external diagnostic systemdesigned to calibrate implantable apparatus 1. The titrating system maybe a separate box that is connected wired or wirelessly to controller 15of implantable apparatus 1. It may also be integrated into externalprocessing device 21. The titrating subsystem is utilized as prescribedby a clinician to ensure that implantable apparatus 1 achieves adequatelevels of stimulation, and to tune up implantable apparatus 1 as thepatient's physiology changes due to age or weight loss.

The titrating system may include a variety of sensors to provideadditional physiological data. Due to the proximity of hypoglossal nerve3 to the internal carotid artery and vein, pressure transducers (notshown) can be easily fitted to one or both of these vessels during thesame surgical procedure. These pressure transducers may be positioned inclose proximity or in direct contact with the vessels for very accuratemeasurements, or nearby in adjacent tissue. In fact, if implantableapparatus 1 itself is implanted in the neck, the pressure transducer canbe incorporated therein, or can be enclosed therein in such a mannerthat it senses the pressure of the surrounding tissue. A carotid arterysensor (not shown) may be added to provide arterial blood pressure datato the system.

The jugular vein pressure is also physiologically important, and canprovide data that closely approximates right atrial pressure. Patientswith heart failure may benefit from their clinicians having this dataavailable in disease assessment and management. A pressure sensor (notshown) can be used to measure the beating of the heart, and can be usedto provide cardiac parameters such as heart rate, heart rate variabilityand certain arrhythmias. These are clinically important because sleepdisordered breathing has been shown to cause cardiovascular stressthrough the sympathetic nervous system activation and intra-thoracicpressure modulation.

Pulsus paradoxus (the rise and fall of arterial and venous pressure dueto changes in intra-thoracic pressure from breathing) can also bedetermined with the pressure sensor, and provide to the system as anindication of respiration. This can be useful if the respiratory signalon the hypoglossal nerve is weak, or in determining the temporalrelationship of pre-inspiratory signal 23 versus respiration. Wideswings in pulsus paradoxus indicate obstruction (increased negativeintrathoracic pressure during inspiration if the airway is obstructed),whereas absent pulsus paradoxus can indicate central apneas. Anadvantage of using a pressure sensor in the neck is that the sensor canbe placed within the same surgical exposure, and does not requireintrathoracic placement and running a lead to the stimulator.Importantly, wide swings in pulsus paradoxus can be quantified, andprovide an indication of AHI (Apnea Hypopnea Index) or events per unittime to the clinician to indicate therapeutic efficacy.

With reference to FIG. 2 and with continuing reference to FIG. 1,monitoring contact 7 continuously monitors the electroneurogram activity(ENG) of hypoglossal nerve 3 beginning at time t₀. Prior to thecommencement of the inspiration cycle at time t₁, controller 15 detectsa pre-inspiratory drive signal 25 from the signals supplied bymonitoring electrode 7. Pre-inspiratory drive signal 25 is a spike inthe hypoglossal nerve activity signal that is generated by the centralnervous system and propagated to the hypoglossal nerve prior to theonset of inspiration. However, the drive signal may be any detectablecharacteristic of the electroneurogram activity indicative of thebreathing cycle. At this point, controller 15 causes stimulating contact9 of cuff 5 to electrically stimulate hypoglossal nerve 3 in response tothe pre-inspiratory drive signal to prevent occlusion of the patient'supper airway. At time t₂, the patient's respiratory cycle converts frominhalation to exhalation. Prior to time t₃, the first respiratory cycleends and a pre-inspiratory drive signal 25 signaling the start of asecond respiratory cycle is detected. Controller 15 again causesstimulating contact 9 of cuff 5 to electrically stimulate hypoglossalnerve 3 in response to the pre-inspiratory drive signal. At time t₄, thesecond respiratory cycle converts from inhalation to exhalation.Implantable apparatus 1 monitors hypoglossal nerve 3 and stimulates thenerve in response to the detected pre-inspiratory drive signal 25thereby preventing occlusions in the upper airway of the patient. Thecontroller may monitor the hypoglossal nerve continuously.Alternatively, the controller may monitor the nerve on a periodic basisto conserve energy.

One unique aspect of the present invention is that the controller usesthe detected pre-inspiratory signal to control stimulation. As seen inFIG. 2, the breathing cycle and the pre-inspiratory signal are bothperiodic with substantially the same periodicity. These two signals areout of phase relative to one another. As noted above, the hypoglossalnerve may be stimulated by stimulating the electrode a given time afterthe pre-inspiratory signal was detected. Ideally, stimulation willcoincide with inspiration. However, stimulation may lead or lag theonset of inspiration. Alternatively, the controller may stimulateproximate in time to a subsequent inhalation to provide ample time toprocess the detected pre-inspiratory signal.

Although the present invention contemplates that a single cuff may beused to both monitor and stimulate a single hypoglossal nerve. Thepresent invention also contemplates using a pair of cuffs on eachhypoglossal nerve. One cuff may be used to monitor one hypoglossal nervewhile the other cuff may be used to stimulate the other hypoglossalnerve. Alternatively, this invention also contemplates a bilateralsystem that would utilize a cuff capable of both monitoring andstimulating. A pair of cuffs may be utilizes with one on eachhypoglossal nerve. In yet a further alternative, a pair of cuffs may beused on a single nerve with one cuff having the monitoring electrode andthe other cuff having the stimulating electrode.

With reference to FIG. 3, and with continuing reference to FIGS. 1 and2, a flow-diagram illustrating the operation of an implanted implantableapparatus 1 is illustrated. The method commences by advancing from astart step 30 to an optional step 31 wherein accelerometer 17 sends asignal to controller 15. Controller 15 processes the signal to detectthe position of the patient's body. At step 32, if the patient isdetermined to be in the supine position (or alternate selected positionor positions), the method advances to step 33. If the patient isdetermined to be in a different position, the method returns to step 31and continues to detect the patient's position until the patient isdetermined to be in the supine position.

Once the patient is found to be in the supine position, controller 15activates monitoring contact 7 of cuff 5 to begin monitoring hypoglossalnerve 3. Hypoglossal nerve 3 is continuously monitored (step 34) until apre-inspiratory drive signal (step 35) is detected. At step 36,controller 15 sends a signal to stimulation contact 9 of cuff 5 tostimulate hypoglossal nerve 3 in response to the detectedpre-inspiratory drive signal. The method then returns to monitoring step34 until accelerometer 17 determines that the patient is no longer inthe supine position.

Optional activation steps 31 and 32 may be replaced by several differentmethods for activating implantable apparatus 1. For instance, it is wellknown in the field of actigraphy that patients showing no movement maybe considered to be asleep. This parameter also gives an indication ofambulation. Therefore, patient motion, as determined by accelerometer17, is important in the determination of sleep/wake state, and is thusused to turn on and turn off implantable apparatus 1. Patient motiondata may also be communicated to the health care provider viacommunication link 23 to establish whether implantable apparatus 1 isadequately benefiting the patient. Alternatively, accelerometer 17 maybe utilized to monitor airway vibrations. When airway vibrations aredetected due to snoring, for instance, controller 15 can causeimplantable apparatus 1 to turn on and begin monitoring hypoglossalnerve 3.

Another method that may be used to initiate monitoring by monitoringcontact 9 of cuff 5 is the use of an algorithm to monitor the cyclicnature of the electroneurogram (ENG). Controller 15 learns the patternof the respiratory cycle based on the ENG obtained from hypoglossalnerve 3. Controller 15 can then use this information to determine when apatient is sleeping and provide a signal to stimulation contact 9 ofcuff 5 to begin stimulation of hypoglossal nerve 3 at this time.

While several embodiments of cuff 5 have been described hereinabove,this is not to be construed as limiting the present invention as the useof any suitable electrode for stimulating and monitoring the hypoglossalnerve has been envisioned.

While several embodiments of a hypoglossal nerve stimulation apparatusand methods associated therewith were described in the foregoingdetailed description, those skilled in the art may make modificationsand alterations to these embodiments without departing from the scopeand spirit of the invention. Accordingly, the foregoing description isintended to be illustrative rather than restrictive. The inventiondescribed hereinabove is defined by the appended claims and all changesto the invention that fall within the meaning and the range ofequivalency of the claims are embraced within their scope.

Although the invention has been described in detail for the purpose ofillustration based on what is currently considered to be the mostpractical and preferred embodiments, it is to be understood that suchdetail is solely for that purpose and that the invention is not limitedto the disclosed embodiments, but, on the contrary, is intended to covermodifications and equivalent arrangements that are within the spirit andscope of the appended claims.

1. A method of treating sleep disordered breathing in a patient,comprising: monitoring the patient for a pre-inspiratory drive signalindicative of the breathing cycle by sensing electroneurogram activityof a hypoglossal nerve of the patient; and electrically stimulating thehypoglossal nerve of the patient following each detection of thepre-inspiratory drive signal.
 2. The method of claim 1, wherein thehypoglossal nerve is electrically stimulated after a preset period oftime elapses from detection of the pre-inspiratory drive signal.
 3. Themethod of claim 1, wherein the hypoglossal nerve is monitoredcontinuously for the pre-inspiratory drive signal.
 4. The method ofclaim 1 further comprising: amplifying the sensed electroneurogramactivity of the hypoglossal nerve to obtain an amplifiedelectroneurogram signal; and using the amplified electroneurogram signalto trigger the direct electrical stimulation of said hypoglossal nerve.5. The method of claim 1, further comprising: sensing a body position ofthe patient; and initiating monitoring of the patient when the patientis determined to be in a lying down position.
 6. The method of claim 5,wherein the lying down position comprises a supine, prone, or side-lyingposition.
 7. The method of claim 1, further comprising connecting astimulating nerve electrode to the hypoglossal nerve so that the nerveelectrode at least partially encircles the hypoglossal nerve.
 8. Themethod of claim 7, wherein the stimulating nerve electrode comprises atleast first and second contacts and the step of electrically stimulatingthe hypoglossal nerve comprises passing electrical stimulation pulsesbetween first and second contacts of the nerve electrode and throughtissue of the hypoglossal nerve.
 9. The method of claim 7, wherein theelectroneurogram activity of the hypoglossal nerve is sensed with athird contact of the nerve electrode.
 10. A method of stimulating ahypoglossal nerve of a patient for the treatment of sleep disorderedbreathing, comprising: continuously monitoring the hypoglossal nerve ofthe patient; detecting a pre-inspiratory drive signal from thehypoglossal nerve indicative of the breathing cycle, the pre-inspiratorydrive signal being generated by the central nervous system andpropagated to the hypoglossal nerve prior to the onset of inspiration;and electrically stimulating the hypoglossal nerve in response to thedetected pre-inspiratory drive signal to prevent occlusion of thepatient's upper airway.
 11. The method of claim 10, wherein thehypoglossal nerve is electrically stimulated after a preset period oftime elapses from detection of the pre-inspiratory drive signal.
 12. Themethod of claim 10, further comprising: amplifying the detectedpre-inspiratory drive signal; and electrically stimulating thehypoglossal nerve in response to the amplified pre-inspiratory drivesignal.
 13. The method of claim 12, wherein the pre-inspiratory drivesignal is amplified by increasing the frequency, amplitude, or acombination thereof of the detected pre-inspiratory drive signal. 14.The method of claim 12, wherein the amplified pre-inspiratory drivesignal triggers the electrical stimulation of said hypoglossal nerve.15. The method of claim 12, further comprising: sensing a body positionof the patient; and continuously monitoring of the patient only when thepatient is determined to be in a lying down position.
 16. The method ofclaim 15, wherein the lying down position comprises a supine, prone, orside-lying position.
 17. The method of claim 10, further comprisingconnecting a stimulating nerve electrode (5) to the hypoglossal nerve sothat the nerve electrode at least partially encircles the hypoglossalnerve.
 18. The method of claim 17, wherein the stimulating nerveelectrode comprises at least first and second contacts and the step ofelectrically stimulating the hypoglossal nerve comprises passingelectrical stimulation pulses between first and second contacts of thenerve electrode and through tissue of the hypoglossal nerve.
 19. Themethod of claim 18, wherein the monitoring the hypoglossal nerve (3) ofthe patient comprises monitoring the electroneurogram activity of thehypoglossal nerve with a third contact of the nerve electrode.
 20. Themethod of claim 1, wherein the pre-inspiratory drive signal comprises asignal generated by the central nervous system and propagated to thehypoglossal nerve prior to the onset of inspiration.
 21. A method oftreating sleep disordered breathing in a patient, comprising: detectinga pre-inspiratory drive signal by sensing electroneurogram activity of ahypoglossal nerve of the patient, the pre-inspiratory drive signalcomprising a signal generated by the central nervous system andpropagated to the hypoglossal nerve prior to the onset of inspiration;and electrically stimulating the hypoglossal nerve of the patient inresponse to the detection of the pre-inspiratory drive signal.